Jacques, Frédéric M. B.; Su, Tao; Spicer, Robert A.; Xing, Yaowu; Huang, Yongjiang; Wang, Weiming and Zhou, Zhekun
Leaf physiognomy and climate: Are monsoon systems different?
Global and Planetary Change, 76(1-2),
Our understanding of past climatic changes depends on our ability to obtain reliable palaeoclimate reconstructions. Climate Leaf Analysis Multivariate Program (CLAMP) uses the physiognomy of woody dicot leaf assemblages to quantitatively reconstruct terrestrial palaeoclimates. However, the present calibrations do not always allow us to reconstruct correctly the climate of some regions due to differing palaeofloristic histories. Present calibrations are also inappropriate for regions experiencing strong monsoon regimes. To help solve this problem, we have established a new calibration that can accommodate monsoonal climates in Asia. Our new calibration is based on the Physg3brcAZ dataset with 45 new Chinese sites added. These Chinese sites are taken from humid to mesic vegetations across China, and all are influenced by monsoonal conditions to some extent. They plot in a distinct part of physiognomic space, whether they are analysed as passive or active samples. The standard deviations for the new monsoonal calibration (1.25 °C for MAT and 217.7 mm for GSP) are in the same range as those observed for previous calibrations. The new monsoonal calibration was tested using a cross validation procedure. The estimates derived from the new monsoonal calibration (PhysgAsia1) for the Chinese sites are more accurate than those obtained from the Physg3brcAZ calibration, especially for the moisture related parameters. The mean absolute error for GSP of the Chinese sites is 294.6 mm in the new monsoonal calibration, whereas it was 1609.6 mm in the Physg3brcAZ calibration. Results for the three wettest months and three driest months are also more accurate and precise, which allows us to study the seasonality of the precipitation, and hence the monsoon. The new monsoonal calibration also gives accurate results for enthalpy reconstruction. Enthalpy is a parameter that is used for palaeoaltimetry, the new calibration is therefore useful for studies of land surface height changes in China, height changes which in turn can affect the strength of the monsoon.
The new monsoonal calibration was tested on two fossil sites from the Late Miocene of southwestern China, namely the Lincang and Xiaolongtan palaeofloras. A comparison of results from the new monsoonal calibration and the Physg3brcAZ calibration shows that there is no strong difference in temperature estimates for the two calibrations, but there is a strong difference in the moisture related parameters. The use of this new monsoonal calibration is recommended for palaeoclimate reconstructions in China.
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